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The Hard X-ray Recovery of the Symbiotic Star, CH Cygni

ATel #2046; K. Mukai (NASA/GSFC/CRESST & UMBC), J. A. Kennea (PSU), G. J.M. Luna (CfA), J. L. Sokoloski (Columbia)
on 11 May 2009; 23:23 UT
Credential Certification: Koji Mukai (mukai@milkyway.gsfc.nasa.gov)

Subjects: X-ray, Request for Observations, Cataclysmic Variable

Referred to by ATel #: 2192, 2245, 2394

After at least 18 months in a hard X-ray faint state, in which RXTE/PCA flux values were comparable to the estimated systematic uncertainties in the PCA background model, CH Cygni has begun steadily brightening in the 2-10 keV band. We have been monitoring CH Cyg with RXTE since 2007 July, with a pointing every 3 weeks. It is strongly detected in the last three pointings (since 2009 March) at 2-10 keV flux above 10-11 ergs cm-2s-1. The PCA light curve is available at http://asd.gsfc.nasa.gov/Koji.Mukai/chcyg/fluxes.gif.

CH Cyg is a symbiotic star with a well-known history of bright, variable hard X-ray emission. Ezuka et al. (1998, ApJ 499, 388) reported the spectacular two component spectrum of CH Cyg based on the ASCA observation taken in 1994: the X-ray emission consists of a soft, unabsorbed component detected below ~2 keV and a hard, highly absorbed component dominant above 3 keV. The 2-10 keV flux was 6.3x10-11 ergs cm-2s-1. During the Suzaku observations in 2006 (once in January, and once in May), however, it was found to be in a hard X-ray faint/soft X-ray bright state. It is likely that the CH Cyg remained in this state through 2008.

This RXTE monitoring campaign is intended in part to allow us to trigger our approved slow TOO observation with Chandra/HETG, once CH Cyg recovers to >70% of the ASCA level. We encourage ground-based observers to obtain optical/IR photometry and spectroscopy over the next few months to detect the multi-wavelength signatures of the hard X-ray recovery of CH Cyg.

RXTE Monitoring of the Symbiotic Star, CH Cyg